This proposal requests funds to modify and upgrade and existing cyclotron facility at Memorial Sloan - Kettering Cancer Center (MSKCC). The cyclotron, a Cyclotron Corp. Model CS-15, produces short-lived, posltron-emitting radionuclides essential for imaging and tissue radioassay studies by three funded PHS- supported grants and a funded Department of Energy Grant. The present proposal is designed to ensure ongoing development of the cyclotron as a key resource for investigation of tumor growth, metabolism and response to treatment, as well as the physiology and metabolism of non-malignant tissues and organs of the tumor- bearing host. Funding is requested for the major pieces of equipment required for the proposed upgrade (items 1 -5 below). The specific aims are: 1. Replacement of cyclotron magnet coils. 2. Replacement of present cyclotron harmonic coils with a modern harmonic coil-centering coil combination and replacement of coil power supplies. 3. Improvement of cyclotron ion source by replacement of power supply and improvement of positioning mechanism. 4. Implementation of system for remote change of cyclotron frequency. 5. Modification of the two existing radiochemical hot cells to create a third hot cell in order to facilitate simultaneous use. 6. Installation of devices (extraction probe and exit slits) for monitoring of parameters affecting cyclotron beam extraction efficiency. 7. Repair of cyclotron helium -3 recovery system. 8. Improvement of cyclotron vacuum by repair of leaks inaccessible without major disassembly of cyclotron. 9. Implementation of radiation detection system within hot cells to permit step-by-step monitoring of yields in radiosynthetic processes. These improvements will enhance the operation of the Cyclotron Facility by increasing the time available for cyclotron bombardment and improving the efficiency of the radiochemical hot laboratory. The proposed upgrade is required to meet the needs of the funded users and to promote pilot studies for new users, as well as to provide opportunities for researchers from neighboring scientific institutions.